Nirmala is one of the few woman officers who have made it to the rank of Rear Admiral or above in the Indian Navy. She is the first woman officer in the Indian Armed Forces to graduate from the National Defence College, New Delhi.

Nirmala is the sister of Nirupama Rao, the current Foreign Secretary of India. The two were known as the 'Menon sisters.’ Nirmala Kannan, along with her sister Nirupama Rao, used to perform at college functions in Bangalore University in the 1960s and 70s. However, music took a backseat with one of the sisters joining the Indian Foreign Service and the other the Armed Forces.

Rear Admiral Nirmala recently assumed charge as the Command Medical Officer (CMO) of the Southern Naval Command, Kochi. Her father wanted one of them to join the Indian Army as he served the nation. On the basis of her performance in the interview they suggested her to join the Navy.

A postgraduate in obstetrics and gynaecology, she served as the Command of Navy hospital INHS Kalyani and Executive Officer of INHS Kalyani and INHS Asvini. She was the Executive Officer of INHS Kalyani from 1995 to 1997.

Rear Admiral Nirmala Kannan is the wife of ViceAdmiral B Kannan. Nirmala Kannan's son, Capt Akshai Kannan, is a dentist with the Army Medical Corps.